Many species of orchids are found in Minnesota prairies, but only three are prairie specialists: western prairie fringed orchid, Great Plains ladies’ tresses, and small white lady’s slipper. They all occur in lime-rich sediments deposited by glaciers and in clay-rich soils of glacial lake beds.
Small white lady’s slipper (Cypripedium candidum) is widely scattered but uncommon across the Great Lakes states to the Dakotas and adjacent Canadian provinces. Minnesota is the core area of the species and may have more individual plants than all other states and provinces combined. It is found in relatively undisturbed, high-quality prairies in the western, southern, and metro regions of the state.
Small white lady’s slipper produces small flowers that are easily overlooked. The best time to see it in bloom is … right now, the last week of May in southern Minnesota and the first or second week of June in the north.
Expandere Wildlife Management Area (WMA) is an 896-acre reserve in intensively farmed southwestern Minnesota. It has what may be the state’s largest population of small white lady’s slipper (Cypripedium candidum), a species of special concern. A survey in 2005 found more than 6,000 plants here. Another survey in 2012 counted 9,373 plants. Powesheik skipperling (Oarisma powesheik), a small, federally endangered butterfly, has also been recorded on this site. A survey in 1993 and 1994 found 5 individuals on this site. However, according to the U.S. Fish and Wildlife Service, the skipperling “may have been extirpated from the Dakotas, Minnesota and Iowa within the last 10 years…”. Surveys in 2014 found the skipperling only at a few sites, and only in a single county in Michigan.
Expandere WMA has two separated units which lie on an area of glacial till, an unsorted aggregate of clay, sand, gravel, and boulders. It is mostly wet prairie. It is bisected by an unnamed stream and has large areas of cattail marsh to the east. There is also an elevated ridge of moderately moist (mesic) prairie to the south. The low areas are subject to flooding in the spring with snow melt and throughout the year after heavy rains, but experience draw-downs in the summer.